Method and apparatus for implementing automated electronic package transmission line characteristic impedance verification

ABSTRACT

A method and apparatus are provided for implementing automated electronic package transmission line characteristic impedance verification. A sinusoidal voltage source is coupled to a transmission line test structure for generating a selected frequency. Impedance measuring circuitry is coupled to the transmission line test structure for measuring an input impedance with an open-circuit termination and a short-circuit termination. Characteristic impedance calculation circuitry is coupled to the impedance measuring circuitry receiving the input impedance measured values for the open-circuit termination and the short-circuit termination for calculating characteristic impedance. Logic circuitry is coupled to the characteristic impedance calculation circuitry for comparing the calculated characteristic impedance with threshold values for verifying acceptable electronic package transmission line characteristic impedance.

FIELD OF THE INVENTION

The present invention relates to a method and apparatus for implementingautomated electronic package transmission line characteristic impedanceverification.

DESCRIPTION OF THE RELATED ART

For the design of transmission lines in electronic packages, one of themost critical parameters to control is the characteristic impedanceZ_(O). The characteristic impedance of transmission lines in electronicpackages with high interconnect densities is most commonly measuredusing time-domain techniques such as time-domain reflectometry (TDR).TDR techniques assume a particular time-domain input excitationwaveform, namely, a fast edge transition with a known rise time.

FIG. 1 illustrates the setup for such TDR characteristic impedancemeasurement techniques. The characteristic impedance is then calculatedby analyzing the waveform at the near-end of the transmission line beingtested.

The disadvantages of this approach include the following:

(A) Complex and expensive electronic test instrumentation is required togenerate and measure the input excitation waveform.

(B) Analysis of the transmission line's near-end waveform is relativelycomplex and requires subjective analytic interpretation, and thus isoften not convenient for a production manufacturing environment.

(C) The time-domain input signal has multiple frequency components,leading to an inherent ambiguity in the frequency at which thecharacteristic impedance measurement was performed.

Other known techniques for measuring characteristic impedance of atransmission line use a frequency-domain approach, featuring anexcitation waveform with only a single sinusoidal frequency component.Such techniques have the advantage of measuring the characteristicimpedance at one particular frequency of interest.

FIGS. 2A and 2B illustrate the setup for one such frequency-domaintechnique that involves two measurements of the input impedance of atransmission line. The first measurement is done with the transmissionline terminated in an open circuit as shown in FIG. 2A. The secondmeasurement is done with the transmission line terminated in a shortcircuit as shown in FIG. 2B.

Typically, the technique illustrated in FIGS. 2A and 2B has been appliedin a laboratory environment to discrete transmission line structures,such as coaxial cables, and not in a production test environment toelectronic packages with high interconnect densities, i.e., those withmultiple transmission line structures.

A need exists for an effective mechanism for implementing automatedelectronic package transmission line characteristic impedanceverification.

SUMMARY OF THE INVENTION

A principal object of the present invention is to provide a method andapparatus for implementing automated electronic package transmissionline characteristic impedance verification. Other important objects ofthe present invention are to provide such method and apparatus forimplementing automated electronic package transmission linecharacteristic impedance verification substantially without negativeeffect and that overcome many of the disadvantages of prior artarrangements.

In brief, a method and apparatus are provided for implementing automatedelectronic package transmission line characteristic impedanceverification. A sinusoidal voltage source is coupled to a transmissionline test structure for generating a selected frequency. Impedancemeasuring circuitry is coupled to the transmission line test structurefor measuring an input impedance with an open-circuit termination and ashort-circuit termination. Characteristic impedance calculationcircuitry is coupled to the impedance measuring circuitry receiving theinput impedance measured values for the open-circuit termination and theshort-circuit termination for calculating characteristic impedance.Logic circuitry is coupled to the characteristic impedance calculationcircuitry for comparing the calculated characteristic impedance withthreshold values for verifying acceptable electronic packagetransmission line characteristic impedance.

BRIEF DESCRIPTION OF THE DRAWINGS

The present invention together with the above and other objects andadvantages may best be understood from the following detaileddescription of the preferred embodiments of the invention illustrated inthe drawings, wherein:

FIG. 1 is a schematic diagram illustrating a prior art time-domainreflectometry (TDR) characteristic impedance measurement technique;

FIGS. 2A and 2B are diagrams illustrating prior art frequency-domaincharacteristic impedance measurement technique;

FIGS. 3 and 4 are schematic diagrams illustrating alternative apparatusfor implementing automated electronic package transmission linecharacteristic impedance verification in accordance with the preferredembodiments; and

FIG. 5 illustrates an electronic unit in accordance with a preferredembodiment of the apparatus of FIGS. 3 and 4.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

In accordance with features of the preferred embodiment, a method isprovided for verifying an electronic package's characteristic impedancethrough the utilization of a single electronic integrated circuitdevice, thereby making its measurement very repeatable and easilyinterpretable in a production manufacturing environment.

Having reference now to the drawings, two embodiments of the inventionare provided and illustrated in FIGS. 3 and 4. In FIG. 3, there is shownapparatus for implementing automated electronic package transmissionline characteristic impedance verification generally designated by thereference character 300 in accordance with one preferred embodiment. InFIG. 4, there is shown apparatus for implementing automated electronicpackage transmission line characteristic impedance verificationgenerally designated by the reference character 400 in accordance withanother preferred embodiment. In both embodiments 300, 400, one or moretest traces are built into the electronic package design and theninternal circuitry of an electronic integrated circuit respectivelydefining apparatus 300 or apparatus 400 analyzes these traces toactively determine the characteristic impedance.

Both apparatus 300 and apparatus 400 consolidate the various electroniccomponents required for the method illustrated in FIGS. 2A and 2B into asingle integrated circuit device. Both apparatus 300 and apparatus 400allow electronic package transmission line characteristic impedanceverification in an automated fashion and in a production ormanufacturing environment.

Apparatus 300 has the advantage of a simpler integrated circuit (IC)design, at the expense of possible losses in accuracy due to variationbetween the two required transmission line test structures, implementedat the package level with open-circuit termination and short-circuitterminations, respectively. Apparatus 400 has the advantage of greateraccuracy due to the requirement of only a single transmission line teststructure, at the possible expense of a more complicated IC design dueto the addition of circuitry for providing the required open-circuittermination and short-circuit termination, in a sequential manner andthe like.

Apparatus 300 of the preferred embodiment consolidates electroniccomponents into an integrated circuit including an open circuit (Z_(OC))impedance measuring circuitry 302, a short circuit (Z_(SC)) impedancemeasuring circuitry 304, and a respective associated sinusoidal voltagesource 306, 308. Apparatus 300 includes a characteristic impedancecalculation block 310 coupled to the impedance measuring circuitry 302,304 receiving the input impedance measured values Z_(OC) and Z_(SC) forcalculating characteristic impedance Z_(O).

From transmission line theory, it is known that for a given line oflength l.Z _(OC) =Z _(O) coth(α+jβ)*l, andZ _(SC) =Z _(O) tanh(α+jβ)*l

Then the characteristic impedance Z_(O), is calculated from the measuredvalues of input impedance measured values Z_(OC) and Z_(SC), as follows:Z _(O)=(Z _(SC) ·Z _(OC))^(1/2)

One significant advantage of this method for calculating thecharacteristic impedance Z_(O) at characteristic impedance calculationblock 310 of apparatus 300 is that it inherently accounts fortransmission line attenuation and dispersion mechanisms, i.e., lossylines are automatically covered.

Apparatus 300 includes logic circuitry 312 coupled to the characteristicimpedance calculation block 310 receiving the calculated characteristicimpedance Z_(O) and control tolerances Z₁, Z₂ representing the limits ofthe characteristic impedance specification are required inputs. A simplepass/fail criteria, represented by Z₁<Z_(O)<Z₂, is implemented by logiccircuitry 312 and the pass/fail results are displayed by a display 314,which allows any operator on the production floor to easily verify theparticular package meets the specification. For example, display 314 isimplemented by pair of light emitting diodes (LEDs) to display the passor fail result.

Referring to FIG. 4, apparatus 400 includes an impedance measuringcircuitry 402 coupled to an open circuit and short circuit terminationcircuitry 404, and a sinusoidal voltage source 406. Apparatus 400includes a characteristic impedance calculation block 408 coupled to theimpedance measuring circuitry 402 receiving the input impedance measuredvalues Z_(OC) and Z_(SC) for calculating characteristic impedance Z_(O).Apparatus 400 includes logic circuitry 410 coupled to the characteristicimpedance calculation block 408 receiving the calculated characteristicimpedance Z_(O) and control tolerances Z₁, Z₂ representing the limits ofthe characteristic impedance specification are required inputs. A simplepass/fail criteria, represented by Z₁<Z_(O)<Z₂, similarly is implementedby logic circuitry 410 and the pass/fail results are displayed by adisplay 412.

Referring to FIG. 5, there is shown an electronic unit generallydesignated by the reference character 500 in accordance with a preferredembodiment. Electronic unit includes a single integrated circuit device502 and a card or multi-chip module 504. In apparatus 300, the singleintegrated circuit device 502 includes the impedance measuring circuitry302, 304; the sinusoidal voltage sources 306, 308; the characteristicimpedance calculation block 310, logic circuitry 312, and display 314.In apparatus 400, the single integrated circuit device 502 includes theimpedance measuring circuitry 402; the open circuit and short circuittermination circuitry 404, sinusoidal voltage source 406,characteristicimpedance calculation block 408, logic circuitry 410, and display 412. Atransmission line test structure 506 representing conductors on the cardor multi-chip module 504 respectively defines the transmission line teststructures #1, #2 of FIG. 3 or the single transmission line teststructure of FIG. 4. The single integrated circuit device 502 ofapparatus 300 and of apparatus 400 is located on or is included in thecard or multi-chip module 504 for the respective transmission line teststructures.

Several advantages of the method of the invention implemented withapparatus 300 and apparatus 400 over the commonly used time-domainmethod of FIG. 1 include the following:

(A) Expensive test instrumentation is no longer needed on the productionfloor to verify that transmission lines meet the required characteristicimpedance requirement.

(B) Any test inconsistencies between equipment and equipment operatorsare eliminated, as well as subjective analysis of the results.

(C) The characteristic impedance can be measured and validated atsingle, discrete frequency(ies) of interest, i.e., the ambiguities infrequency content inherent in time-domain methods are eliminated.

While the present invention has been described with reference to thedetails of the embodiments of the invention shown in the drawing, thesedetails are not intended to limit the scope of the invention as claimedin the appended claims.

1. A method for implementing automated electronic package transmissionline characteristic impedance verification comprising the steps of:providing a transmission line test structure, said transmission linetest structure representing conductors on a card, providing a singleintegrated circuit device disposed on said card; said single integratedcircuit device implementing automated electronic package transmissionline characteristic impedance verification steps including; generating aselected frequency coupled to said transmission line test structure;measuring an input impedance with an open-circuit termination and ashort-circuit termination on said transmission line test structure;using said input impedance measured value for said open-circuittermination and said short-circuit termination, calculatingcharacteristic impedance; and comparing said calculated characteristicimpedance with threshold values for verifying acceptable electronicpackage transmission line characteristic impedance.
 2. A method forimplementing automated electronic package transmission linecharacteristic impedance verification as recited in claim 1 includes thesteps of providing a pair of said transmission line test structuresrespectively implemented at a package level with a open-circuittermination and a short-circuit termination.
 3. A method forimplementing automated electronic package transmission linecharacteristic impedance verification as recited in claim 2 wherein thesteps of measuring said input impedance with said open-circuittermination and said short-circuit termination for said transmissionline test structure includes the steps of providing said singleintegrated circuit device with open-circuit impedance measuringcircuitry coupled to one of said pair of said transmission line teststructures; and providing said single integrated circuit device withshort-circuit impedance measuring circuitry coupled to another of saidpair of said transmission line test structures.
 4. A method forimplementing automated electronic package transmission linecharacteristic impedance verification as recited in claim 1 includes thesteps of providing a single transmission line test structure implementedat a package level and providing said single integrated circuit devicewith open-circuit and short-circuit termination circuitry coupled tosaid single transmission line test structure at said package level.
 5. Amethod for implementing automated electronic package transmission linecharacteristic impedance verification as recited in claim 4 wherein thesteps of measuring said input impedance with said open-circuittermination and said short-circuit termination for said transmissionline test structure includes the steps of sequentially providing anopen-circuit termination and a short-circuit termination to said singletransmission line test structure utilizing said open-circuit andshort-circuit termination circuitry.
 6. A method for implementingautomated electronic package transmission line characteristic impedanceverification as recited in claim 1 includes the steps of displaying apass or fail result responsive to said compared values.
 7. Apparatus forimplementing automated electronic package transmission linecharacteristic impedance verification comprising: a sinusoidal voltagesource coupled to a transmission line test structure for generating aselected frequency; impedance measuring circuitry coupled to saidtransmission line test structure for measuring an input impedance for anopen-circuit termination and a short-circuit termination; characteristicimpedance calculation circuitry coupled to said impedance measuringcircuitry for receiving said input impedance measured values with saidopen-circuit termination and said short-circuit termination forcalculating characteristic impedance; logic circuitry coupled to saidcharacteristic impedance calculation circuitry for comparing saidcalculated characteristic impedance with threshold values for verifyingacceptable electronic package transmission line characteristicimpedance; said sinusoidal voltage source, said impedance measuringcircuitry, said characteristic impedance calculation circuitry, and saidlogic circuitry being implemented by a single integrated circuit device;and said transmission line test structure represents conductors on acard and said single integrated circuit device is disposed on said card.8. Apparatus for implementing automated electronic package transmissionline characteristic impedance verification as recited in claim 7 whereinsaid transmission line test structure includes a pair of transmissionline test structures respectively implemented at a package level with aopen-circuit termination and a short-circuit termination.
 9. Apparatusfor implementing automated electronic package transmission linecharacteristic impedance verification as recited in claim 8 wherein saidimpedance measuring circuitry includes an open-circuit impedancemeasuring circuitry coupled to one of said pair of transmission linetest structures; and a short-circuit impedance measuring circuitrycoupled to another of said pair of transmission line test structures.10. Apparatus for implementing automated electronic package transmissionline characteristic impedance verification as recited in claim 7 whereinsaid transmission line test structure includes a single transmissionline test structure implemented at a package level and an open-circuitand short-circuit termination circuitry coupled to said singletransmission line test structure.
 11. Apparatus for implementingautomated electronic package transmission line characteristic impedanceverification as recited in claim 7 includes a display coupled to saidlogic circuitry for displaying a pass or fail result responsive to saidcompared values.
 12. Apparatus for implementing automated electronicpackage transmission line characteristic impedance verification asrecited in claim 7 wherein said characteristic impedance calculationcircuitry calculates said characteristic impedance represented by:Z _(O)=(Z _(SC) ·Z _(OC))^(1/2) where Z_(O) represents said calculatedcharacteristic impedance and Z_(OC) and Z_(SC) represent said inputimpedance measured values for said open-circuit termination and saidshort-circuit termination.
 13. Apparatus for implementing automatedelectronic package transmission line characteristic impedanceverification as recited in claim 7 wherein said logic circuitry comparessaid calculated characteristic impedance with threshold values forverifying acceptable electronic package transmission line characteristicimpedance represented by:Z₁<Z_(O)<Z₂ where Z_(O) represents said calculated characteristicimpedance and Z₁, Z₂ represent lower and upper threshold values for anelectronic package characteristic impedance specification.
 14. Anelectronic unit comprising: a transmission line test structure; and asingle integrated circuit device for implementing automated electronicpackage transmission line characteristic impedance verification; saidsingle integrated circuit device including: a sinusoidal voltage sourcecoupled to said transmission line test structure for generating aselected frequency; impedance measuring circuitry coupled to saidtransmission line test structure for measuring an input impedance for anopen-circuit termination and a short-circuit termination; characteristicimpedance calculation circuitry coupled to said impedance measuringcircuitry for receiving said input impedance measured values with saidopen-circuit termination and said short-circuit termination forcalculating characteristic impedance; logic circuitry coupled to saidcharacteristic impedance calculation circuitry for comparing saidcalculated characteristic impedance with threshold values for verifyingacceptable electronic package transmission line characteristicimpedance; and said transmission line test structure representsconductors on a card and said single integrated circuit device isdisposed on said card.
 15. An electronic unit comprising: a transmissionline test structure; and a single integrated circuit device forimplementing automated electronic package transmission linecharacteristic impedance verification; said single integrated circuitdevice including: a sinusoidal voltage source coupled to saidtransmission line test structure for generating a selected frequency;impedance measuring circuitry coupled to said transmission line teststructure for measuring an input impedance for an open-circuittermination and a short-circuit termination; characteristic impedancecalculation circuitry coupled to said impedance measuring circuitry forreceiving said input impedance measured values with said open-circuittermination and said short-circuit termination for calculatingcharacteristic impedance; logic circuitry coupled to said characteristicimpedance calculation circuitry for comparing said calculatedcharacteristic impedance with threshold values for verifying acceptableelectronic package transmission line characteristic impedance; and saidtransmission line test structure represents conductors on a multi-chipmodule and said single integrated circuit device is included in saidmulti-chip module.